1. Field of the Invention
The present invention relates to insulative fabric materials and particularly to thermally insulative fabric materials having substantial loft.
2. Description of Related Art
It is recognized that the ability of an insulative layer to entrap a large amount of air improves its thermal insulative properties. Until recently, some of the best materials to provide these properties were natural insulations, such as wool or feathers.
While natural insulations have many advantages, these materials likewise have many deficiencies. Wool is heavy, it is prone to odor, it is uncomfortable against one's skin, and it has limited loft. On the other hand, feathers and down are lofty and warm when dry, but are easily compromised by damp, they are expensive and difficult to contain, their loft is easily lost, and they cause allergic reactions in some.
To address some of these concerns, various synthetic insulations have been developed. Many of these products comprise polymer fibers or fabrics which effectively hold warmth by entrapping air within their mesh, yet are easy to use, light, durable, hypoallergenic, non-odor forming, and sometimes breathable. Examples of such materials are sold by Minnesota Mining and Manufacturing Co. (3M), of St. Paul, Minn., under the trademark THINSULATE, and by E. I. dupont de Nemours and Company (Dupont), of Wilmington, Del., under the trademark THERMOLITE.
While these materials are successful in part, they continue to suffer from a number of deficiencies. Synthetic insulations still lack the high loft which has for so long been coveted. Loft can be produced, but it is often at the cost of many layers of material with intrinsic added weight. Furthermore, many synthetic insulations lack resilience to deformation--losing warmth when mass is applied against them.
In an effort to improve these properties, further development efforts have continued. U.S. Pat. No. 4,118,531, granted to Hauser Oct. 3, 1978, teaches that a batting or webbing of polyester or polypropylene microfibers (around 10-15 microns in diameter) can be produced with good thermal properties. To brace these fibers against compression, a larger crimped fiber is incorporated into the microfiber batting to improve resilience and reduce matting of the fibers over time. Nonetheless, the amount of resilience to deformation of this composite is limited to the bulk fiber's ability to maintain its crimp. Additionally, the bulk of these fibers is believed to restrict their useful applications.
Still another improvement in fiber loft is sought, this time in a stretchy fabric material, in U.S. Pat. No. 4,551,378 issued Nov. 5, 1985 to Carey, Jr. Bicomponent fibers are taught which can be crimped and bonded together. However, further improvement in resilient loft is still believed possible.
In WIPO Application WO 93/00390, published 7 January 1993, owned by 3M, energy expandable microspheres are mixed with a fibrillated polyolefin matrix suspension and then expanded to produce a thermally insulative membrane. With the expandable microspheres embedded in fibrils of the fibrillated polyolefin, an expanded polyolefin sheet material is produced by applying energy to expand the microspheres. A light, breathable, thermally insulative material can be produced using this process. Moreover, the insulative material produced is quite resilient to deformation.
Regretfully, the processing of insulation in the manner taught by WO 93/00390 continues to be constrained. To be effective, a fibrillated polyolefin is required, inasmuch as expansion of the insulation is dependent upon embedding the expandable microspheres within the linked microscopic fibrils of such material. More burdensome is the fact that presently available microsphere technology is keenly limited in its temperature range--with deterioration or complete destruction of the microspheres normally occurring at temperatures above about 200.degree. C. when exposed for more than a few minutes. Such temperature limitations restrict many desirable processing steps, such as sintering, which would otherwise be advisable with a polymer material alone.
A number of other patents have taught that microspheres can be combined with a binder material in order to adhere them together, sometimes for thermally insulative applications. For instance, U.S. Pat. No. 3,615,972 to Morehouse, Jr., et al. teaches how to produce a variety of expandable microspheres and the use of different binder or coating materials to hold such microspheres in place. Similarly, U.S. Pat. No. 5,155,138 to Lundgvist also teaches expandable microsphere formation but again teaches its use with a binder material. U.S. Pat. No. 4,929,020 to Takashima et al. teaches use of expandable microspheres in a coating composition that serves as a binder.
The problem with all such previous attempts to use expandable microspheres with a binder material is that the binder materials tend to limit many desirable properties of the thermal insulation. For example, binder material can add undesirable bulk, weight, and stiffness to an insulated article. Moreover, binder displaces air, reducing thermal insulative efficiency and restricting air permeability or "breathability". Finally, binder may also limit the compressibility or recoverability of the insulative material.
Despite these deficiencies, prior to the present invention, expandable microspheres have been applied as a thermal insulative material only when adhered together or to another material using some form of adhesive binder. The use of spheres alone or unadhered in thermal insulation has not been previously suggested, much less some method for accomplishing such a task.
Accordingly, it is a primary purpose of the present invention to produce an insulative material that is lightweight, durable, highly thermally insulative, and resilient to deformation.
It is another purpose of the present invention to produce an insulative material that retains significant thermal insulative properties even when wet or placed under compressive force.
It is still another purpose of the present invention to produce an insulative material that provides resilient properties with a wide variety of insulative materials.
It is a further purpose of the present invention to produce an insulative material that provides resilient properties of thermoplastic microspheres without limiting the initial processing procedures for the insulative materials.
These and other purposes of the present invention will become evident from review of the following specification.